The invention involves an electrical temperature sensor with a resistance layer containing platinum as a measuring resistor provided with electrical connections on an electrically insulating surface of a ceramic substrate, wherein the resistance layer is provided with at least one layer to protect against contamination or damage. In addition, the invention involves in another embodiment an electrical temperature sensor, whose resistance layer for protection against contamination or damage is provided with a multiple layer, which has an electrically insulating intermediate layer and an outer covering layer. Furthermore, the invention relates to a method for manufacturing a temperature sensor with a platinum-containing resistance layer, which is applied and structured in the form of a thin layer on an electrically insulating surface of a ceramic substrate.
As a multiple layer, according to European patent EP 0 327 535 B1, column 2, lines 20-25, a protective covering, consisting of several layers, of a platinum thin-film resistance thermometer is indicated. A multiple layer of this type can have, for example according to lines 26-31, a dielectric layer as an electrically insulating intermediate layer and an outer covering layer.
From European patent EP 0 327 535 B1, a temperature sensor having a thin-film platinum resistance is known. There, the temperature measuring resistance made of platinum is formed on a surface of an electrically insulating substrate, wherein the resistance element is covered with a dielectric protective layer, which preferably consists of silicon dioxide and has a thickness in the range of 2000-4000 Angstroms. In addition, as the covering layer, a diffusion barrier layer is provided, which is applied by deposition of titanium in an oxygen atmosphere for formation of titanium oxide. This barrier layer has a thickness in the range of 6000-12000 Angstroms. Even if the diffusion barrier layer allows the entry of oxygen to the dielectric layer and thus for the most part prevents an attack of nascent metal ions from the glass layer on the platinum layer, extreme ambient conditions can nevertheless lead to an attack on the platinum layer, so that its physical behavior as a temperature measuring resistor is disturbed.
In addition, an electrical measuring resistor for resistance thermometers, as well as a process for manufacturing such an electrical measuring resistor, is known from U.S. Pat. No. 4,050,052 or the counterpart German patent DE 25 27 739 C3.
An object of the invention is to protect the measuring resistor against external chemical or mechanical attacks and, in particular, to ensure that no entry whatsoever of contamination from the outer atmosphere into the measuring resistor is possible. This object is achieved for an electrical temperature sensor according to a first embodiment of the invention in that, on the resistance layer, an intermediate layer is applied as a diffusion barrier layer, wherein on the side of the resistance layer facing away from the substrate surface and spaced therefrom, an electrode is applied.
Proving to be especially advantageous is the longer lifetime, while at the same time, a relatively cost-effective manufacture is possible, so that the temperature sensor is also suitable as a mass-produced product. Advantageous forms and modifications of the temperature sensor of the first embodiment are described below and in the dependent claims.
The thickness of the intermediate layer preferably lies in the range of 0.2 xcexcm to 30 xcexcm. The total height of the temperature sensor lies in the range of 0.1 to 1 mm, while its major surface area has a length in the range of2 to 15 mm and a width in the range of 0.5 to 6 mm. The temperature sensor carrier with the mounted chip element has the following geometric outer dimensions: total height of the module in the range of 0.3 to 3 mm, wherein the major surface area has a length of 4 to 80 mm and a width of 2 to 12 mm.
The electrode is preferably made of a platinum-containing layer, in particular an additional platinum layer. In a preferred form of the first embodiment, the additional platinum layer is covered by a passivation layer. Preferably, at least a part of the passivation layer is here located between the additional platinum layer and the resistance layer. Such an arrangement has the advantage that the resistance layer is protected from the outside by the passivation layer and is electrically insulated, while the intermediate layer represents an insulation layer between the resistance layer and the platinum layer.
In another advantageous form of the first embodiment, the additional platinum layer is applied on a carrier substrate arranged opposite to and spaced from the measuring resistor. The additional platinum layer here preferably covers a supply line to the measuring resistor, which is applied on the carrier substrate. Furthermore, in an advantageous form, the additional platinum layer is galvanically separated from the supply line by an insulation layer. It proves to be advantageous here that the platinum layer can be biased electrically negative relative to the resistance layer or the supply line, and in addition, the covering of the supply line represents an additional protection.
For protection from an undesired bypass formation between the measuring resistor contacts, caused by the condensation of electrically conducting particles (soot), it has proven to be especially advantageous to seal a gap, between the measuring resistor and the carrier substrate lying opposite it, on all sides using an electrically insulating materialxe2x80x94preferably sealing glass.
The object is achieved for an electrical temperature sensor according to the second embodiment of the invention with a platinum-containing resistance layer as a measuring resistor provided with electical contacts on an electrically insulating surface of a ceramic substrate, wherein the resistance layer for protecting against contamination or damage is provided with a multiple layer, that has an electrically insulating intermediate layer and an outside covering layer, wherein the intermediate layer is constructed as a diffusion barrier layer, which has aluminum oxide, magnesium oxide or tantalum oxide or a mixture of two materials of these oxides or a multiple layer system, wherein the covering layer is made as a passivation layer.
Proving to be especially advantageous is the simple and cost-effective design, so that the temperature sensor according to the invention can be manufactured as a mass-produced product. Advantageous forms and modifications of the temperature sensor of the second embodiment are described below and in the dependent claims.
The covering layer is preferably made of glass. In an advantageous form of the second embodiment the covering layer comprises a mixture of silicon oxide, barium oxide and aluminum oxide, wherein the weight ratio of the three oxides lies in the range of 35:50:15. The actual ceramic substrate is preferably made of aluminum oxide.
The thickness of the intermediate layer lies in the range of 0.2 xcexcm to 30 xcexcm, while the outer covering layer has a thickness in the range of 10 to 30 xcexcm. The thickness of the entire coating (as a multiple layer) lies in the range of 10.5 to 60 xcexcm.
The total height of a temperature sensor according to the second embodiment lies in the range of 0.1 to 1 mm. Its major surface area has a length in the range of 2 to 15 mm and a width in the range of 0.5 to 6 mm. The geometry of the temperature sensor, constructed according to the second embodiment, on the carrier (module) results in the same ranges for height, length and width as has already been described for the first embodiment.
Proving to be further advantageous is the miniaturized construction method, so that the temperature sensor can also be implemented directly in the exhaust gas for motor vehicle applications up to 1100xc2x0 C., wherein because of the miniaturization, a redundancy circuit of several temperature sensors is also possible, so that the reliability of the measurement or control system is improved considerably. In addition, the thermal behavior is improved.
Furthermore, in a preferred form of the second embodiment of the invention, an electrode is applied on the side of the resistance layer facing away from the substrate surface outside of the intermediate layer, wherein between the electrode and the resistance layer at least one part of the passivation layer is located. The electrode here is preferably located between the passivation layer and the intermediate layer. Furthermore, in a preferred form, the electrode can be encased by the passivation layer.
The electrode is preferably made of a platinum-containing layer, in particular of an additional platinum layer. It is also possible to arrange the additional platinum layer on the side of the passivation layer facing away from the resistance layer. An advantage thereby results in that the additional platinum layer protects the resistance layer against atmospheric poisoning in the sense of a xe2x80x9csacrificial electrodexe2x80x9d.
In a further form, the additional platinum layer is provided with an electric connection. Here, it is possible to electrically negatively bias the platinum layer relative to at least one connection of the measuring resistor. It proves to be advantageous therein that the platinum poisons present as positive ions in extreme ambient conditions (Si ions and metal ions) are drawn to the negative platinum layer.
The object is further achieved for a process for manufacturing an electrical temperature sensor with a platinum-containing resistance layer, which is applied and structured in the form of a thin layer on an electrically insulating surface of a ceramic substrate, in that after completion of the structuring, the resistor is provided with a multiple layer for protection against contamination or damage, wherein by use of shading masks for receipt of free contact surfaces, at least one diffusion barrier layer is applied as an intermediate layer, and spaced from the resistance layer an electrically conducting layer is applied as an electrode. As the electrode, a platinum-containing layer, in particular a platinum layer, is preferably applied.
Advantageous forms of the process are described below and in the dependent claims.
Here, the thin layer is preferably structured by the application of a pre-formed photoresist mask and converted by means of ion etching. A structured thin layer has the advantage that, with minimal material usage and on small surfaces, high ohmic resistances can be produced. The described structuring technique is to be preferred over the previously used laser meander process, since the structures produced hereby have very clean structure edges without rim damage. The structures have very long term stability and ideally permit themselves to be tightly covered with a diffusion barrier layer by an adjustable flank steepness (e.g., ramp-shaped).
It has proved advantageous to manufacture the the diffusion barrier layer by thin layer technology, which is applied after the removal of the photoresist mask. By means of thin layer technology the layers may be applied hermetically sealed. The diffusion barrier layer can also be applied by screen printing or plasma spraying. By the use of shading masks, a structure can be applied with the desribed process, such that an expensive and cost-intensive structuring process for obtaining free contacts is dispensed with. In a preferred form of the process, the electrically conducting layer is applied on the diffusion barrier layer as an electrode with connection contacts by use of shading masks by means of a PVD or sputtering process.
It is, however, also possible to apply the electrically conducting layer by means of a screen printing process. This process is preferably used if the electrically conducting layer is applied on a carrier substrate arranged opposite the temperature sensor.
Furthermore, a passivation layer is advantageously applied by means of screen printing on the electrically conducting layer serving as an electrode. The screen printing process proves to be particularly expedient and cost-effective for this purpose.
In the manufacturing process, several blanks of ceramic can form a composite multi-unit substrate, which can be simultaneously cost-effectively coated and only divided by sawing after application of the passivation layer.
In a preferred form, according to both the first and the second embodiments of the invention, the ceramic substrate is made of Al2O3. Furthermore, according to both embodiments, the intermediate layer is preferably also made of Al2O3, MgO or a mixture of the two materials, wherein the weight proportion of Al2O3 lies in the range of 20% to 70%. It is further possible to construct the intermediate layer of a layer sequence of at least two layers, each of which is formed of at least one oxid from the the group Al2O3, MgO, Ta2O5. At least one layer can thereby be made from two of the mentioned oxides, wherein preferably a physical mixture of oxides if used. However, it is also possible to use mixed oxides.
In another embodiment of the invention, the group of oxides consisting of Al2O3, MgO, Ta2O5 can be expanded to include hafnium oxide.
Preferable, the intermediate layer consists of a one-layer system according to Table 1, with the materials given as items 1 to 6, or of a multiple layer system according to Table 2, that has at least two layers 1 and 2, wherein however, on layer 2 another layers or several layers can be joined. The different coating materials are designed in the individual items or lines with numbers 7 to 30.
The use of these materials proves to be especially advantageous, because these metal oxides are still stable at high temperatures. The intermediate layer is preferably manufactured using a PVD-, CVD-, IAD-, IBAD-, PIAD-, or magnetron-sputter-process, wherein the abbreviations mean:
PVD: Physical Vapor Deposition
CVD: Chemical Vapor Deposition
IAD: Ion Assisted Deposition
IBAD: Ion Beam Assisted Deposition
PIAD: Plasma Ion Assisted Deposition.
Furthermore, the passivation layer according to the two embodiments is a mixture made of SiO2, BaO and Al2O3, wherein the weight proportion of SiO2 lies in the range of 20% to 50%. It proves to be advantageous that this mixture has a high insulation resistance.